In general, devices for removing the tread of worn tires, commonly referred to as buffers or raspers, are known. See, for example, Pelletier, U.S. Pat. No. 3,867,792, issued Feb. 25, 1975; Mattox et al., U.S. Pat. No. 3,877,506, issued Apr. 15, 1975; Weir, U.S. Pat. No. 3,965,959, issued Jun. 29, 1976; and Morris et al., U.S. Pat. No. 4,116,256, issued Sep. 26, 1978.
Tire buffing is part of the tire retreading procedure. Typically, the tire casing to be retreaded is buffed to remove excess rubber, to provide a substantially evenly textured crown for receiving a cured tread strip and to provide a predetermined shoulder profile.
Tire casings usually include a belt package (a package of steel belts or cables) underlying the road engaging surface (e.g., the original tread) of the tire. Prior to retreading, the casing must be buffed, generally to a predetermined characteristic crown radius corresponding to the upper contour of the belt package. The casing is buffed to leave only a predetermined thickness, e.g. 3/32 of an inch, of material remaining over the top belt. The shoulder of the casing is also buffed (trimmed) to eliminate or reduce voids or patterns in the shoulder created by the original tread, and to provide a relatively straight profile between the casing side walls and the crown. A worn casing from each of the various models and sizes of new tires has a characteristic crown width, crown buffing radius and shoulder trim angle which must be created as an initial step in the buffing process.
A suitable layer of bonding material, such as uncured cushion gum, optionally including a low temperature vulcanizing agent and accelerator, is placed over the crown, then a cured tread strip, typically of a width corresponding to the width of the crown of the casing is cut to the length corresponding to the casing circumference and is disposed over the casing crown. Alternatively, continuous replacement treads in the shape of a ring (i.e., ring treads) have also been used to retread the buffed casing. A roller pressing process, commonly referred to as stitching, is next performed on the assembly to force air from between the tread strip and casing. The assembly is then subjected to heat and pressure, generally in an autoclave, to cure the bonding layer.
In the process of retreading tire casings with cured treads utilizing a cushion gum binder in a low temperature process, the face of the casing which receives the replacement tread can be buffed to a predetermined crown radius within a relatively small tolerance. Additionally, with the advent of new replacement tread designs, such as the contoured replacement tread disclosed in U.S patent application Ser. No. 07/634,421, filed Dec. 27, 1990, and owned by the assignee of this application, it is also necessary to ensure that the shoulder radius is also buffed precisely to a predetermined arc or radius. Known buffing machines do not permit highly controlled buffing of the compound radius in an efficient manner.
In particular, known devices cannot easily be used to buff a worn casing to a compound radius. In normal operation of one known device, the rasp is moved into contact with a rotating tire. As the rasp removes the worn tread, it is moved back and forth across the crown surface of the tread. Once a sufficient amount of rubber has been removed, i.e., until about 3/32 of rubber remains above the cords, the rasping is halted. The rasp is then pivoted with respect to the casing so that the rasp can be moved into contact with a first shoulder of the tire carcass, and buffing of that shoulder is accomplished. Then the rasp is moved so it can work on the other shoulder of the tire casing to buff, and thus final buffing steps occur.
Other known devices are configured so that a rotating casing can be articulated and moved into contact with a rotating rasp. See, e.g., U.S. Pat. No. 3,877,506. In either case, however, a number of movements are required to complete the buffing operation and to establish the desired crown radius and shoulder radius. Moreover, the rasp and/or tire must be repeatedly adjusted so that the orientation of the particular component results in formation of the desired radii. The procedures are especially pronounced if a compound radius system is to be used.
Various devices have been proposed to overcome these deficiencies. For example, use of a tire profile template for the particular size and shape of the casing to be retreaded is proposed in the aforementioned U.S. Pat. No. 4,116,256. In this device, the template engages a guide surface, which normally lies in a plane that is tangential to the surfaces of the cutting wheels. The template is shifted axially of the cutting wheels as necessary, to enable the texturizing wheels to finish the shoulder areas of the casing. However, the use of templates is undesirable because different templates are needed for each different tire size or desired tire profile. Preparation, storage and use of different templates is expensive and cumbersome.
Alternatively, a buffing apparatus mounted for movement in an arcuate path generally parallel to the axis of rotation is shown in the aforementioned U.S. Pat. No. 3,867,792. The buffer guide shown in that patent consists of a rigid arcuate plate forming a concave surface facing the tire mounting unit and rollers adapted to roll along the surface. This complex structure is expensive to manufacture and difficult to use.
While these devices have overcome some of the deficiencies in the prior art, there is still a long felt need for a buffing device which is easy to use and which is less complex than those discussed above.